The distribution of a single program, so that a portion of the program executes on more than one computer, has become more pervasive as “desktop” computers have become more powerful. FIG. 1 demonstrates an example of a computer network containing several distributed computers upon which au application can execute. While most computer networks are many orders of magnitude larger, this small network is used as at example. Presently, many computer systems allow objects to communicate over a network. One method of distributing object oriented programs across computer networks is Automatic Object Distribution (AOD), described in the commonly assigned, copending patent application having Ser. No. 08/852,263, now U.S. Pat. No. 6,157,960, entitled “Technique for Programmatically Creating Distributed Object Program”.
When a distributed object-oriented program is built with AOD, it is written as if the entire system is to reside on a single machine and compiled into unlinked executable code, known as “byte code.” The distribution of the objects is determined, and the AOD process is used to effect the distribution by analyzing the aforementioned byte code, determining which method calls will be made across the computer network, and generating proxy objects to represent remote objects and their method calls. Two proxies are created for each object-to-object call that will occur over the network: one that resides on the machine containing the object making the call, and one that resides on the machine containing the object to which the call is made. These two proxies cooperate to hide the fact that the objects actually reside on different machines from the programmer, thereby sparing the programmer any need to be aware of the distributed nature of the system when writing his code.
When calls are made across a computer network in this fashion, the parameters are objects. When these objects represent finite data, such as arrays, data structures, integers, etc. they are passed using well-known techniques such as Object Serialization. In Object Serialization, all the pieces of the object are combined and converted to a byte stream, which is sent across the network and then reassembled into a new data object on the other side of the network connection. This method is well-known in the art, and is used by the AOD system to send parameters for method calls which are split across the network.
However, some types of data objects do not lend themselves to Object Serialization. In particular, objects which represent data streams and complex objects (which may contain extensive programmed methods and/or references to other objects, have system locking requirements, or do not implement a serialization protocol) do not lend themselves easily to object serialization.
Objects which represent data streams are not a finite size, as they often represent data to be read from or written to some data source, such as a diskette drive. Additionally, since they may represent data being input to or output from a system or peripheral device, the data they contain may be in a system-specific format. When a program is distributed with AOD, different parts of it may be distributed to different types of computers, which may have incompatible data formats.
Additionally, under the AOD proxy system, if one data stream object is split and proxied, all data streams must be so split and proxied, because the proxy remaining on the first machine would contain method names and semantics that are identical to those in a real data stream, causing name collisions. These name collisions would eliminate the possibility of any kind of data input or output operations on a machine on which a data stream proxy resides, a result which is not acceptable in today's environment. If the name collision problem were to be overcome, the performance of the proxied data stream would not be acceptable, as each read or write on a data stream so proxied would require two method calls and a remote method call.
When complex objects are passed as parameters on remote method calls, it is undesirable to pass them as simpler objects would be passed, using serialization, for three reasons:
1. A complex object will likely contain extensive code and/or references to other objects. To serialize the object, all of the data it contains and the objects it references must be serialized and passed over the network as a byte stream. This may be inefficient, especially if the object is being passed to allow access to only a small percentage of its data.
2. When a complex object is passed over the network to be used by another object, it must be locked on its “home” machine. This is to prevent any other objects from invoking it, which may result in changes to the data contained therein, while it is being operated on in a remote machine. Without such locking, the object may become corrupted. For example, if an object contains a counter, and the object is invoked on a remote machine to increment the counter and also invoked on the local machine to increment the same counter, then when the remote copy is returned and recopied over the original copy, the counter's value will be one less than required. Locking imposes a performance penalty on all objects that need to access the object being serialized, as they are all required to queue up and wait for the remote operation on the object to complete and for the results to be returned and recopied.
3. A complex object that is to be serialized must contain special code to enable such serialization. For example, in the Java™ (Java is a trademark of Sun Microsystems) environment, the object must implement the serializable interface. This may require the programmer to be aware of and code for the distributed nature of the program.